1. Field of the Invention
This invention relates to the field of spectrometry, and more particularly to a method and apparatus for holographic spectrometry.
2. Description of the Related Art
Upon excitation of atomic particles in an object, the particles may emit electromagnetic radiation having certain spectral characteristics. Interpretation of this emitted radiation may provide information on the molecular energy levels of the material forming the object, molecular geometries of the material, molecular bonding, as well as other information. By comparing the spectral information emitted by the object with known spectral characteristics, it is possible to determine the chemical composition and structure of the material as well as to permit quantitative chemical analysis.
There are two general approaches used in measuring spectral information. Under the dispersive approach, received electromagnetic radiation passes through a prism or a grating to separate the radiation into component wavelengths. The component wavelengths are then individually measured and recorded. Under the interferometric approach, the electromagnetic radiation is divided into two or more paths and then recombined to form an interference pattern. Spectral information can then be obtained by measuring and recording the interference pattern.
In one form of interferometric spectrometry known as real-time holographic spectrometry, a wave of electromagnetic radiation which has been stored in a hologram inteferes with a subsequent wave of electromagnetic radiation. The interference pattern which is generated by the interference of the waves can then be interpreted to give spectral information. One such holographic spectrometer disclosed in Kawata, "Fourier Transform Spectrometer With a Self-Scanning Photodiode Array", Applied Optics, v. 23 n. 2 (1984) uses conventional optics to generate spectral information using fast Fourier transform techniques.
While such holographic spectrometers are somewhat effective, they were generally not fabricated from integrated optics and therefore were relatively large and costly. In addition, holographic spectrometers fabricated from conventional optics could not generally be used for imaging applications. Further, infrared holographic spectrometers were not generally cooled during operation and therefore tended to generate large amounts of thermal radiation which would often interfere with the operation of the elemental detectors. Even those holographic spectrometers which are cooled generally require relatively large devices to adequately remove the thermal energy generated by the spectrometers.